Navigational instrument

ABSTRACT

A Hall-effect transducer mounted on the axis of rotation of the magnet of a shipboard or aircraft magnetic compass produces a time-varying electrical signal having magnitude proportional to the sine of the angle between a preselected heading of the craft and the actual heading at any moment. The signal, and its timeintegral which is proportional to the off-course distance of the craft at constant speed, are displayed on indicating meters for the use of the pilot in steering or are applied to control an automatic steering system.

United States Patent Lloyd [54] NAVIGATIONAL INSTRUMENT Edward C. Lloyd,8624 Red Coat Lane, Potomac, Md. 20854 [22] Filed: Feb. 26, 1970 [21]Appl.No.: 14,367

[72] Inventor:

[52] US. Cl ..3l8/647, 3 118/653, 33/222 [51] Int. Cl ..G05f l/00 [58]Field ofSearch ..3l8/653,647,587, 588,580;

[56] References Cited UNITED STATES PATENTS 3,517,285 6/1970 Kundler..3l8/588 2,924,886 2/1960 Cullen ..33/222 [4 1 Apr. 18, 1972 2,403,0917/1946 Lear ..3l8/647 X 3,551,706 12/1970 Chapman ..324/045 X 3,197,8808/ 1965 Rice et a1. ..324/045 X 3,425,648 2/1969 Wipff et a1. ..324/045X Primary Examiner-Benjamin Dobeck 57 ABSTRACT A Hall-effect transducermounted on the axis of rotation of the magnet of a shipboard or aircraftmagnetic compass produces a time-varying electrical signal havingmagnitude proportional to the sine of the angle between a preselectedheading of the craft and the actual heading at any moment. The signal,and its time-integral which is proportional to the off-course distanceof the craft at constant speed, are displayed on indicating meters forthe use of the pilot in steering or are applied to control an automaticsteering system.

3 Claims, 2 Drawing Figures 7 HIGH DEGREES PATENTEUAPR 18 I972 INVENTOREdward C Llg/d NAVIGATIONAL INSTRUMENT BACKGROUND OF THE INVENTION.

' The invention relates to a navigational instrument, for shipboard oraircraft use, having electrical output voltages of magnitude anddirection corresponding to the heading error and to the cumulative netlateral deviation of the craft from a preselected course, such outputvoltages being applied to provide a display for use of a pilot insteering or to control an automatic steering system. In particular, theinvention relates to an instrument of this type that depends for itsaction upon an electrical signal derived from the action of a magneticcompass element upon a Hall-effect transducer so placed and orientedthat this signal'is directly proportional to the sine of the angle ofdeviation of thecraft heading from a preselected heading, and in whichsuch signal is integrated with respect to time. Assuming constant speed,the lateral distance error of the craft from its intended course at anytime is proportional to I I sin Zdt,

where Z is the instantaneous value of the angle between the preselectedheading and the actual heading, and t is the elapsed time from the startof the run.

In the normal process of steering an aircraftor watercraft along apreselected course, either manually or automatically, deviations of theheading from the preselected course inevit'ably occur due to actionofthe elements on the craft, the necessity for steering around obstacles,and the like. In the use of the usual indications or signals from aconventional compass such deviations may be corrected to the extent ofreturning the craft to the initial heading, but it is not practicable todetermine from the compass the lateral distance that the craft has beendisplaced from the original course-line. Thus the craft will, ingeneral, be steered on a succession of courses parallel to the originalcourse-line. The corresponding lateral displacements will oftenaccumulate predominately in one direction, thereby causing substantialdeparture of the craft from the intended'line of travel.

The display of off-course distance information in combination with thedisplay of ofl course angle information enhances the utility of bothtypes of information by facilitating their rapid assimilation by thepilot without the necessity for his reading and interpreting a compasscard. Alternatively, the control of an automatic steering system by asignal derived from the combination of these two quantities permits thesystem to be operated so as to return the craft to a preselectedcourse-line as Well as to a preselected heading, rather than only to apreselected heading as heretofore.

The state of the prior art is illustrated by the following examples. Inone method a transmitting compass is utilized in which the compassmagnet moves between follow-up electrical contacts to provide a signalthat is used to actuate a course recorder (Magnetic Compasses andMagnetometers" by Alfred Hine, U. Toronto Press (1968') p. 174). Inanother method a pair of magnetometers, sensing a component of theearths magnetic field, are used to control the frequency ofvariable-frequency electrical signals that actuate counters to indicatethe cumulative off' course heading. These methods require relativelyelaborate and expensive equipment. The first method suffers further fromthe lack of means for providing a direct indication of off-coursedistance. The present invention overcomes the deficiencies of methodssimilar to that of the first example by deriving a signal from themagnetic field normally present in a magnetic compass without necessityfor the compass magnet to actuate electric contacts, capacitance oroptical sensing systems or the like. The signal so derived, proportionalto the sine of the heading error angle rather than to the angle itselfas in older methods, is then well adapted to direct and simple signalprocessing, display, and

control methods. In schemes using magnetometers, as in the secondexample, serious errors may arise due to changes in the magnitude of themagnetic field component sensed, caused by magnetometer leveling errorsor by local magnetic disturbances, that are not related to changes inthe relative direction of the horizontal component of the earthsmagnetic field. This deficiency is overcome in the present invention bysensing only the angular position of a compass magnet which, in turn, isresponsive only to the direction of the local magnetic field and is notaffected by changes in its magnitude.

BRIEF DESCRIPTION OF THE DRAWING.

FIG. 1 is a representation of one embodiment of the invention whereinthe magnetic compass element and its associated Hall-effect transducerare shown in sectional view, wherein the final signal output ispresented as a visual display utilizing two indicating meters shown infull front view, and wherein electrical circuits interconnecting theHall-effect transducer and the indicating meters are shown in schematicview; and

FIG. 2 is a partial diagrammatic representation of another embodiment ofthe invention, in which an automatic steering system is controlled bysignals derived from the Hall-effect transducer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

An essential component of the invention is a Hall-effect transducerconsisting of a thin slab or wafer, usually rectangular in shape, of asemiconducting material such as germanium, indium arsenide, or indiumantimonide, having a pair of electrical conductors attached to each pairof opposite edges. The plane through the center of the thin slab orwafer, parallel to the largest face, is herein referred to as theprincipal plane of the transducer. When an excitation voltage is appliedto one pair of conductors the resulting current flowing across the waferis laterally deflected by any magnetic field component present that isnormal to the principal plane and that passes through the wafer. Aresulting signal voltage, called the Halleffect voltage, is generated atthe other pair of conductors and is proportional to the excitationcurrent and to the magnitude of such normal magnetic field component.

FIG. 1 shows a conventional magnetic compass assembly 10 that is mountedin an aircraft or watercraft. The assembly 10 includes cylindricalcompass bowl 11, a fixed pivot 12 mounted centrally within the bowl onvertical axis 13, and a pivot cup 14 adapted to support compass magnet15 on pivot 12. Magnet 15, having north-seeking and south-seeking polesl6 and 17, is supported in a stable horizontal position so that the axisof the magnet maintains alignment with the horizontal component of theearths magnetic field. Bowl 11 is partly filled with a liquid 18 thatdamps the movement of the compass magnet and partially supports it bybuoyant effect. Centered in the upper surface of bowl 11 is acylindrical cavity 19 containing a closely fitting hollow plugconsisting of knob 20 and hollow stud shaft 21. Inside the plug is avertical diametral web 22 on which is mounted, in a centered position onvertical axis 13, a Hall-efiect transducer 23 with its principal planeparallel to the plane of web 22. Flexible wires 24 provide electricalconnections to'the four edges of the Hall-effect transducer, asdescribed above. Stub shaft 21 is manually rotatable within cavity 19 bymeans of knob 20 so that the principal.

plane of the Hall-efiect transducer may be set at any selected angleabout axis 13. Lines of magnetic flux extend between the north-seekingand south-seeking poles 16 and 17, and one such line is illustrated bydashed line 25 passing through Halleffect transducer 23. The totalmagnetic flux passing through the Hall-effect transducer is a maximumwhen its principal plane is normal to the axis of magnet 15, and aminimum when this plane is aligned with the magnet axis. The magnitudeof the Hall-effect voltage will be proportional to the magnitude of theflux so intercepted, and thus will be proportional to the sine of theangle between the magnet axis and the principal plane of the transducer,and the polarity of the voltage will depend upon the direction ofangular deviation.

The output display comprises instrument panel 26 on which is mounted adirect current voltmeter 27 having a pointer 28 and a zero-center scale29 marked in degrees of off-course angle. A similar indicator 30 has apointer 31 and a zero-center scale 32 marked in yards of off-coursedistance.

The excitation current for the Hall-effect transducer is supplied by abattery 33 via wires 34. The Hall-effect signal from the Hall-effecttransducer is connected by wires 35 to the input terminals 36, 37 of theoff-course angle indicator 27. The Hall-effect signal is also connected,via wires 35 and 38, to the input of an integrating circuit comprising aresistor 39, capacitor 40, and electronic amplifier 41. The outputterminals 44 and 45 of the integrating circuit are connected to theinput terminals 46, 47 of the off-course distance indicator 30.Amplifier 41 is an operational amplifier, powered by batteries 48connected in the usual manner, and has input terminals 49 and 50 andoutput terminals 44 and 45. The integrating circuit contains a normallyopen reset switch 42 which functions, with current-limiting resistor 43,to pemtit manual setting of the voltage across capacitor 40, and thusthe integrator circuit output voltage, to zero.

In the operation of the embodiment of the invention of FIG. 1, the craftis brought to a desired heading, and knob 20 is then manually turned tochange the angular orientation of transducer 23 until a position isfound in which off-course angle indicator 27 indicates zero, and inwhich an angular deviation of knob 20 is followed by pointer 28 in thesame angular direction. In this position the principal plane ofHall-effect transducer 23 is parallel to the axis of magnet and orientedto produce signals of the proper polarity. Switch 42 is then momentarilyclosed manually, thereby removing any charge that may have accumulatedon integrating capacitor 40 and bringing pointer 31 of off-coursedistance indicator 30 to zero. Thereafter the craft speed is heldconstant, and as the craft yaws or the heading is temporarily changeddue to need for avoidance of obstructions, etc., both the off-coursedistance and the heading error are indicated continuously. When thevessel is brought back to the preselected courseline, the off-coursedistance indication returns to zero, and

' when both pointers are again on zero the vessel is located on thepreselected course-line and has the preselected heading. The off-coursedistance indicator is calibrated in units of distance at a particularspeed, at 10 knots for example, and for higher or lower speeds thedistance indicated is taken to be greater or smaller, respectively, inproportion.

It is to be noted that variation in magnitude of the component of thelocal earths field sensed due,,for example, tilting of the compass or tothe proximity of iron masses, has no significant effect on the operationof the instrument, since the Hall-effect transducer responds to theconstant and relatively large field of the compass magnet rather than tothe earths field directly. The compass magnet, of which the angularalignment is unaffected by changes in magnitude of the earths fieldcomponent sensed, produces a field intensity at the Halleffecttransducer at least two orders of magnitude larger than the total earthsfield, and at least three orders of magnitude larger than apparentchanges in the magnitude of the earths field encountered in practice.Errors due to such apparent changes are correspondingly small.

FIG. 2 shows another embodiment of the invention, in which theHall-effect voltage on wires 35 of FIG. 1 and the time-integratedHall-effect voltage on wires 66 of FIG. 1 are algebraically added andused to servocontrol the heading of the craft. In FIG. 2, 63 is anoperational amplifier of the same type as amplifier 41 of FIG. 1, and issimilarly powered by batteries, not shown. Wires 35 connect the signaloutput from the Hall-effect transducer of FIG. 1 to amplifier inputterminal 61 via resistor 64 and to common terminal 62. Similarly, wires66 connect the integrated Hall-effect transducer signal from tertvoltages. An aerodynamic or hydrodynamic steering surface 71, mounted onshaft 72 which is free to rotate about axis 73, is angularly positionedabout axis 73 by a direct current motor 74 acting through pinion 76 toposition gear sector 77 and its rigidly attached shaft 72. In practice,pinion 76 would be positioned to contact gear sector 77 oppositeterminal 82, but is shown angularly displaced around axis 73 forclarity. An arm 78 is rigidly attached to gear sector 77 and makeswiping electrical contact with an electrical resistance wire 79positioned along the length of a fixed sector 80 that is concentric withgear sector 77. Batteries 81 are connected to the center and ends ofresistance wire 79 so that the voltage existing at any time betweenwiper arm 78 and the center terminal 82 will hive a magnitude dependentupon the angular position of gear sector 77 and wiper arm 78, and apolarity dependent upon which side of the center terminal 82 arm 78rests. This voltage is connected by wires 83 and 84 to the coil of arelay 85 in series with the output signal of amplifier 63, so that thevoltage is opposed by the amplifier output voltage. Relay 85 is athreeposition double-pole relay that maintains a mid-position when thevoltage applied to its coil is small compared to the voltage ofbatteries 81. When a larger voltage is applied to the coil of relay 85it closes one of two pairs of contacts 86 connected so that theresultant direction of rotation of motor 74, driven by current frombattery 87 via two of the relay contacts 86, wires 88 and commutator 75,is such as to turn gear sector 77 and wiper arm 78 in a direction toreduce the voltage applied to the relay coil. The automatic steeringsystem will thus steer the craft in a direction to minimize the outputvoltage of amplifier 63 which, in turn, requires that both theHall-effect voltage and the integrated value of the Hall-effect voltageapproach zero. The resultant off-course distance of the craft is thusmade to approach zero.

In using the embodiment of the invention of FIG. 2, the craft is broughtto the desired heading by manipulating knob 20 with switch 42 heldclosed, thus causing the automatic steering system to vary the headingof the craft until the principal plane of the Hall-effect transducer 23is parallel to the axis of compass magnet 15. Switch 42 is then opened,the speed of the craft is thereafter held substantially constant, andthe automatic steering system maintains the heading so as to minimizethe lateral distance error.

It will be understood, of course, that the fore-going disclosure relatesto preferred embodiments of the invention, and that numerousmodifications may be made therein without departing from the scope ofthe invention as set forth in the appended claims. F or example, forcertain applications the Halleffect transducer may be excited byalternating current, and the resultant Hall-effect alternating currentsignal processed by well-known amplifying and rectifying techniques toobtain the same results herein described. In another modification, theHall-effect voltage may be integrated by a motor having a shaft speedproportional to the applied Hall-effect voltage. In still anothermodification, the Hall-effect voltage may be processed by anelectrochemical method in which the amount of a visible product of anelectrochemical action is proportional to the integral of theHall-effect voltage.

I claim:

1. A navigational system for a craft comprising:

a compass bowl fixedly mounted on said craft;

a fixed pivot mounted within said bowl on a Vertical axis;

a compass magnet supported on said pivot;

a housing rotatably mounted on said compass bowl for manual rotationabout said vertical axis;

a Hall-effect transducer mounted in said housing with its principalplane vertical and in the magnetic field of said compass magnet;

four flexible electrical conductors extending into said housing and eachcontacting a respective edge of said transducer;--

an exciting current source connected to two of said conductorscontacting opposed edges of said transducer; and

the remaining two of said four conductors connected to a first voltmeterwith a zero-center scale whereby, when said craft is set on a course andsaid housing is angularly set so that said first voltmeter indicateszero, deviations of said craft from said course will cause said firstvoltmeter to indicate the off-course angle of said deviations.

2. A navigational system as set forth in claim 1, wherein said remainingtwo conductors are also connected to the input of an integratingoperational amplifier; and

a second voltmeter with a zero-center scale connected to the output ofsaid amplifier whereby, when said craft is set on a course and saidamplifier output is electrically discharged so that said secondvoltmeter indicates zero,

5 including:

an adding operational amplifier having two inputs connected to saidfirst and second voltmeters, respectively; and

means connected to the output of said adding operational amplifier forautomatically navigating said craft so as to reduce the magnitude of thevoltages at both of said voltmeters toward zero.

1. A navigational system for a craft comprising: a compass bowl fixedlymounted on said craft; a fixed pivot mounted within said bowl on aVertical axis; a compass magnet supported on said pivot; a housingrotatably mounted on said compass bowl for manual rotation about saidvertical axis; a Hall-effect transducer mounted in said housing with itsprincipal plane vertical and in the magnetic field of said compassmagnet; four flexible electrical conductors extending into said housingand each contacting a respective edge of said transducer; an excitingcurrent source connected to two of said conductors contacting opposededges of said transducer; and the remaining two of said four conductorsconnected to a first voltmeter with a zero-center scale whereby, whensaid craft is set on a course and said housing is angularly set so thatsaid first voltmeter indicates zero, deviations of said craft from saidcourse will cause said first voltmeter to indicate the off-course angleof said deviations.
 2. A navigational system as set forth in claim 1,wherein said remaining two conductors are also connected to the input ofan integrating operational amplifier; and a second voltmeter with azero-center scale connected to the output of said amplifier whereby,when said craft is set on a course and said amplifier output iselectrically discharged so that said second voltmeter indicates zero,deviations of said craft from said course will cause said secondvoltmeter to indicate off-course distance of said craft at constantspeed of said craft.
 3. A navigational system as set forth in claim 2,and further including: an adding operational amplifier having two inputsconnected to said first and second voltmeters, respectively; and meansconnected to the output of said adding operational amplifier forautomatically navigating said craft so as to reduce the magnitude of thevoltages at both of said voltmeters toward zero.